Golf ball

ABSTRACT

The present invention is a golf ball with a spherical core and a cover with one or more than two layers which covers the core, wherein the core includes two layers including an inner core having a spherical shape with an area formed in the center thereof, and an outer core covering the inner core, wherein value A is equal to or larger than 10.5 and value C is equal to or smaller than 3.7, wherein the value A is the deformation amount (mm) of the ball when the initial load is 98 N (10 kgf) and the ending load is 5880 N (600 kgf), and the value C is the deformation amount (mm) of the ball when the initial load is 98 N (10 kgf) and the ending load is 1275 N (130 kgf). The area is filled with at least one substance being different from the material of the inner core.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2014-262710 which was filed on Dec. 25, 2014. The entire disclosure of Japanese Patent Application No. 2014-262710 is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf ball including a spherical core and a cover with one or more than two layers covering the core, and more in detail, the present invention relates to a golf ball having excellent hitting feeling that satisfies advanced golfers and professional golfers.

2. Description of the Related Art

Recently, as population of golfers has increased, needs of the golfers towards golf balls varies and is personalized. In order to fulfill the needs, various considerations with regards to ball structures have been made. It is ideal for the golf balls to be comprehensively superior in three elements which are soft hitting feeling, distance, and spins.

The hitting feeling being good, when using a driver (#1 wood), means that the entire ball or a part of the ball being largely distorted and the golf ball is knocked hard, or that the golfer feels strong restitution, for example. It is an evaluation of feelings. Often time, plays will be influenced in a good way, when the feeling is good and thus reliability to the golf balls and clubs increases, while hard golf balls gives discomfort. Therefore, in particular, professional golfers and advanced golfers susceptibly feel whether the hitting feeling is hard or soft, and thus they happen to select golf balls which match their feelings in order to obtain better hitting feelings.

Also, among conventionally proposed distance type golf balls with which greater distance can be achieved with drivers, there are many which realize low spins by increasing initial velocity, when being hit, by making a cover harder. However, among the distance type golf balls like this, there are many which are inferior in speed control when using irons and in the hitting feeling. For this reason, there have been efforts to make the hitting feeling soft and better by forming the cover thinner, but that results in having disadvantage in durability against breakage after hitting. Recently, rather than two-piece solid golf balls or three piece solid golf balls, various four-piece solid golf balls and five-piece solid golf balls with multi-layers, such as more than four and five layers, have been suggested in order to comprehensively improve performance of the golf balls to higher quality. For example, Japanese Un-Examined Patent Application Publication No. 2001-231887, Japanese Patent No. 3,362,857, and Japanese Un-Examined Patent Application Publication No. 2005-103264 disclose such balls. Although these golf balls could increase the distance by increasing the ball restitution (initial velocity) and by lowering the spin, and could make the spin amount for approach shots appropriate, importance of the hitting feeling was undervalued, and it was not enough for the professional golfers and the advanced golfers from the standpoint of getting comfortable feeling such as softness and knocking feeling.

The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the described embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein

SUMMARY OF INVENTION

The present invention was made in considering the above identified issues, and has the objective to provide golf balls with which the professional golfers and the advanced golfers can attain soft and comfortable hitting feeling while keeping excellent carry performance.

As a result of making the best effort to attain the above objective, inventors of the present invention, for the golf balls with a cover having one or more than two layers, formed a core to have two layers, which include an inner core being spherical and having an area in the center thereof and an outer core covering the inner core. The area is filled with at least one substance which is different from the material of the inner core. The inventors have found that it is sure for the professional golfers and the advanced golfers to attain the soft and comfortable hitting feeling and consistently maintain excellent carrying performance by making value A and value C within a prescribed range, where the A value is a deformation amount (mm) of the ball, when an initial load is 98 N (10 kgf) and an ending load is 5880 N (600 kgf), and the C value is a deformation amount (mm) of the ball when an initial load is 98 N (10 kgf) and an ending load is 1275 N (130 kgf).

Therefore, the present invention provides the golf balls below.

[1] A golf ball includes a spherical core and a cover with one or more than two layers covering the core. The core includes two layers, one of which is an inner core being spherical and having an area in the center thereof, and the other of which is an outer core covering the inner core. The area is filled with at least one substance being different from a material of the inner core. Value A is larger than or equal to 10.5, and value C is smaller than or equal to 3.7. The value A is a deformation amount (mm) of the golf ball when an initial load is 98 N (10 kgf) and an ending load is 5880 N (600 kgf). The value C is a deformation amount (mm) of the golf ball when an initial load is 98 N (10 kgf) and an ending load is 1275 N (130 kgf). [2] In the golf ball recited in [1], at least one substance selected from a group consisting air, water, polyvinyl alcoholic (PVA) gel, cellulosic gel, oil state fluid, solid paraffin, and a jelly state food is filled in the area of the inner core. [3] In the golf ball recited in [1], the area of the inner core is a spherical space having a diameter between 5 and 18 mm. [4] In the golf recited in [1], an outer diameter of the inner core is between 15 and 25 mm. [5] In the golf ball recited in [1], a diameter of the core is between 34 and 40 mm. m. [6] In the golf ball recited in one of [1], surface hardness (S) of the inner core is between 30 and 90 in JIS-A Hardness. [7] In the golf ball recited in [1], the cover covers the core with two layers, and the two layers are, from inside, an intermediate layer, and an outer most layer. [8] In the golf ball recited in [1], the cover covers the core with three layers, and the three layers are, from inside, a surrounding layer, an intermediate layer, and an outermost layer. [9] In the golf ball recited in [8], hardness (Shore D material Hardness) of the outer most layer is larger than material hardness of the surrounding layer.

According to the golf ball of the present invention, it is guaranteed for the professional golfers and the advanced golfers to attain the soft and the comfortable hitting feeling and maintain excellent carrying performance.

The above and/or other aspects, features and/or advantages of various embodiments will be further appreciated in view of the following description in conjunction with the accompanying figures. Various embodiments can include and/or exclude different aspects, features and/or advantages where applicable. In addition, various embodiments can combine one or more aspect or feature of other embodiments where applicable. The descriptions of aspects, features and/or advantages of particular embodiments should not be construed as limiting other embodiments or the claims.

In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. Unless indicated otherwise, these terms are only used to distinguish one element from another. For example, a first object could be termed a second object, and, similarly, a second object could be termed a first object without departing from the teachings of the disclosure. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to or “on” another element, it can be directly connected or coupled to or on the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). However, the term “contact,” as used herein refers to direct contact (i.e., touching) unless the context indicates otherwise. Terms such as “same,” “planar,” or “coplanar,” as used herein when referring to orientation, layout, location, shapes, sizes, amounts, or other measures do not necessarily mean an exactly identical orientation, layout, location, shape, size, amount, or other measure, but are intended to encompass nearly identical orientation, layout, location, shapes, sizes, amounts, or other measures within acceptable variations that may occur, for example, due to manufacturing processes. The term “substantially” may be used herein to reflect this meaning. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments of the present invention are shown by way of example, and not limitation, in the accompanying figures.

FIG. 1 is a schematic cross-sectional view showing a structure of a golf ball according to the first embodiment of the present invention.

FIG. 2 is an explanatory view to explain a core used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following paragraphs, some embodiments of the invention will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.

Hereinafter, the present invention will be described in detail. The golf ball of the present invention has an internal structure with a spherical core and a cover, with one or more than two layers, which covers the core. Further, the spherical core has a two-layer structure including an inner core being spherical and having an area at the center thereof, and an outer core covering the inner core. The area is filled with at least one substance which is different from the material of the inner core. In detail, the golf ball 1 shown in FIG. 1 has the spherical core 10 and a cover with three layers including, from the inside, a surrounding layer 2, an intermediate layer 3, and an outer most layer 4. The outer most layer has a lot of dimples D on the outer surface. And as shown in FIG. 1, the spherical core 10 of the golf ball has an inner core 11 having an area in the center thereof, and an outer core 12 covering the inner core.

As shown in FIG. 2, the inner core 11 has the area at the center and has an inner diameter D1 and an outer diameter D2. The diameter (outer diameter) D2 of the inner core is preferably larger than or equal to 15 mm, and more preferably larger than or equal to 18 mm, while the upper limit is preferably smaller than or equal to 25 mm and more preferably smaller than or equal to 22 mm. Depending on a material used for the inner core, restitution will be especially decreased, if it is outside the range.

The inner diameter D1 of the inner core is preferably larger than or equal to 5 mm, and more preferably 8 mm, while the upper limit is preferably smaller than or equal to 18 mm, and more preferably smaller than or equal to 15 mm. There is a chance of not getting an effect of having the area, and of lowering the characteristic of the ball itself, especially the durability, if it is outside the range.

With regards to the material of the inner core, a well-known rubber material can be used as a base material. With regards to a base rubber, a well-known base rubber such as natural rubber (NR) or synthetic rubber, more particularly polybutadiene, especially cis-1,4-polybutadiene which has a cis configuration for at least more than 40% is recommended to use primarily. Also, it is possible to use the above mentioned polybutadiene together with natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene rubber (SBR), and the like, if desired.

Also, it is possible to synthesize polybutadiene with rare earths element catalyst such as Nd catalyst, and metal catalyst such as cobalt catalyst and nickel catalyst.

The above mentioned polybutadiene is not particularly limited to a certain type, but it is preferable to have more than or equal to 60 mass percent in the base rubber. If this composition amount is not enough, there may be cases in which a golf ball with excellent restitution is not obtained.

Also, rubbers other than above mentioned polybutadiene can be mixed and used together as long as not missing the objective of the present invention. An example includes natural rubber (NR), nitrile rubber (NBR), styrene-butadiene rubber (SBR), polyisoprene rubber (IR), and ethylene-propylene-diene rubber (EPDM). It is possible to use one of those alone or combine more than two of those.

It is possible to mix unsaturated carboxylic acid and co-cross-linking agent such as metal salt thereof or the like, zinc oxide, barium sulfate, inorganic filler such as calcium carbonate, dicumyl-peroxide, organic peroxide such as 1,1-bis (t-butylperoxy)cyclohexane, or the like to the base rubber. Also, it is possible to add anti-aging agent which is commercially available, if necessary.

Further, thermoplastic resin can be employed as a material for the inner core. For example, thermoplastic resin such as nylon, polyarylate, ionomer resin, polypropylene resin, polyurethane thermoplastic elastomer, polyester-based thermoplastic elastomer, or the like can be used.

The area of the inner core can be filled with air, but also gas, liquid, semi-liquid having viscosity such as gel, or contents such as substances which change forms due to chemical or physical factors. When the area of the inner core is filled with air, the area is a hollow. The contents include, for example, air, water, polyvinyl alcohol (PVA) gel, polymer gel such as polyurethane gel and cellulosic gel, oil state fluid such as paraffin oil and oleic acid, solid paraffin, a jelly state food, and the like. Further, any combination of the above contents can be employed. In this way, by making the above mentioned contents to be infilled into the area of the inner core, it is possible to provide unique, more comfortable, moderately softer hitting feelings, when hitting with the driver (#1 wood).

Methods to fill into the above mentioned area depends on kinds of the contents and characteristic thereof, and includes, for example, pouring and encapsulating various polymer gel to a half cup which is for the inner core, and injecting, by an injector or the like, fluid such as oil, water, or the like to the area of the inner core which is formed in advance.

Here, as shown in FIG. 2, surface hardness (S) of the inner core is not limited, but is preferably between 30 and 90 in JIS-A Hardness, and more preferably between 60 and 80. By adjusting the surface hardness (S) of the inner core within the above mentioned ranges, it can be expected to have enough difference in hardness with surface hardness (S) of the outer core and effects of fewer spins. For example, the difference between the surface hardness (S) of the inner core and the surface hardness (S) of the outer core is preferably between 10 and 20, more preferably between 14 and 17 in JIS-C Hardness (or JIS-A Hardness).

On the other hand, the outer core is a covering layer which directly covers the above mentioned inner core, and has thickness preferably between 1 and 25 mm, and more preferably between 5 and 20 mm.

The material of the outer core can be a well-known rubber material as a base material. For the base rubber, natural rubber or synthetic rubber, more particularly polybutadiene, especially cis-1,4-polybutadiene which has a cis configuration for at least more than or equal to 40% is recommended to use primarily. Also, it is possible to use the above mentioned polybutadiene together with natural rubber, polyisoprene rubber, styrene-butadiene rubber, and the like, if desired.

For a manufacturing method and a vulcanization method of the inner and outer cores, well-known methods employed for two layer core (inner core and outer core) of the golf ball can be used. For example, for the forming method of the inner core, it is possible to appropriately select rubber composition, and it is formed by vulcanizing or hardening in the same way of well-known rubber composition for golf balls. For vulcanization conditions, for example, it is possible to perform with vulcanization temperature between 100 and 200° C., and for vulcanization time between 10 and 40 minutes.

On the other hand, it is possible to employ a well-known method for forming the outer core by using rubber composition, and is not particularly limited; however, methods below can be preferably employed. First, a material for forming the outer core is poured to a predetermined metal mold, and a pair of half cups having semispherical shell shapes is formed by primary vulcanization (semi-vulcanization). Next, the spherical inner core which has been premade is secondarily vulcanized (full vulcanization) in a state in which the inner core is covered by the half cups formed as mentioned above. In other words, it is possible to employ the vulcanization process divided preferably into two stages. Further, it is possible to employ preferably a method of forming by injecting the material for forming the outer core around the inner core.

The diameter (or the outer diameter of the outer core) of the entire core (hereinafter simply expressed as “core”) made by the above mentioned inner core and the outer core is preferable larger than or equal to 30 mm, and more preferable larger than or equal to 34 mm, while the upper limit is preferably smaller than or equal to 40 mm. If it is outside the range, it will be more difficult to form a multi-layer structure on the core, and thus to obtain the best characteristic of the ball.

The deformation amount of the core (the entire core combining the inner core and the outer core), in other words, the deformation amount when the initial load is 98 N (10 kgf) and the ending load is 1275 N (130 kgf), is preferably larger than or equal to 2.0 mm, and more preferably larger than or equal to 2.5 mm, while the upper limit is preferably smaller than or equal to 6.0 mm, and further preferably smaller than or equal to 5.5 mm. If the deformation amount is too small, there will be a case where the hitting feeling is hard. If the deformation amount is too large, there may be cases in which the hitting feeling becomes too soft, and the durability against the ball breakage becomes worse due to peeling off an upper layer of the core when repeatedly hitting.

Next, the cover will be described in detail. The cover is a part covering the core, and includes at least one layer, for example, a two layer cover, or a three layer cover. For the two layer cover, in certain cases, an inner layer is denoted an intermediate layer, and an outer layer is denoted an outer most layer. For the three layer cover, each layer is possibly denoted, from the inside, a surrounding layer, an intermediate layer, and an outer most layer. For example, as shown in FIG. 1, the three layers of the cover is illustrated with the surrounding layer 2 covering the core 10, the intermediate layer 3 covering the surrounding layer 2, and the outer most layer 4 covering the intermediate layer 3. By the way, on an outer surface of the above mentioned outer most layer 4, usually there are a lot of dimples D which enhance aerodynamic characteristic.

It is possible to use a well-known material for the cover as a material in each layer forming the cover. For example, well known thermoplastic resin, ionomer resin, high neutralization resin composition, thermoplastic and thermosetting polyurethane, or thermoplastic elastomer in polyamide system, polyester system, or the like can be listed.

Commercial products can be used when using ionomer resin or high neutralization resin composition for material of each layer of the cover. For example, sodium neutralization type ionomer resin such as HIMILAN 1605, HIMILAN1601, AM 7318 (each of which is manufactured by Mitsui DuPont Polychemical), SURLYN 8120 (manufactured by DuPont), or the like, zinc neutralization type ionomer resin such as HIMILAN1557, HIMILAN 1706, AM 7317 (each of which is manufactured by Mitsui DuPont Polychemical), or the like, trade names “HPF 1000,” “HPF 2000,” “HPF AD 1027,” experimental “HPF SEP 1264-3” of DuPont can be listed. It is possible to use one of those alone or combine more than two of those.

It is possible to use one alone or combine more than two of the above mentioned resin materials, but from the stand point of increasing the restitution, it is possible to use by combining particularly zinc neutralization ionomer resin and sodium neutralization ionomer resin. In this case, compounding ratio of zinc neutralization ionomer resin and sodium neutralization ionomer resin is not particularly limited, but can be usually between 25:75 and 75:25, preferably between 35:65 and 65:35, more preferably between 45:55 and 55:45. If this compounding ratio is outside the above mentioned range, the restitution becomes too low, and thus there may be cases in which performance in distance being in demand is not obtained.

For resin material for each layer of the cover, various additives such as pigment, dispersant, antioxidant, ultraviolent absorbent, ultraviolet stabilizer, mold release agent, plasticizer, inorganic filler (zinc oxide, barium sulfate, titanium dioxide or the like) can be added.

A method for forming each layer of the cover is not limited to a specific method, but well known methods can be employed. For example, a forming method by injecting the material for each layer of the surrounding layer, the intermediate layer, and the outer most layer around the core in series can be employed. Further, a pressing and heating method for between 2 and 15 minutes at the temperature between 140 and 200° C., or the like can be employed, after forming the pair of the half cups having semispherical shell shapes which are made of the material for forming each layer and then wrapping the half cups by an intermediate product (an intermediate sphere made by forming the surrounding layer and the intermediate layer around the core or area surrounding the core).

When the above mentioned core is covered by the surrounding layer, the thickness of the surrounding layer is preferably larger than or equal to 0.5 mm and the upper limit is preferably smaller than or equal to 2.0 mm. If it is outside the range, it will be a reason for decreasing the ball durability due to peeling at a border of the core, depending on the used material.

The material hardness of the above mentioned surrounding layer is not particularly limited, but it is preferable that Shore D Hardness is preferably larger than or equal to 15, and more preferably larger than or equal to 20. Also, the upper limit is not particularly limited, but it is preferably smaller than or equal to 80, and more preferably smaller than or equal to 70. If it is outside the range, the initial velocity of the ball will be decreased, and the hitting feeling will be uncomfortable due to too much knocking feeling, too hard feeling, or the like. The material hardness means hardness when the material is formed in a sheet shape with a prescribed thickness, and the material hardness of each layer which will be described hereinafter means the same.

When the sphere covered by the surrounding layer is covered by the intermediate layer, the thickness of the intermediate layer is preferably larger than or equal to 0.5 mm, and the upper limit is preferably smaller than or equal to 1.5 mm. If it is outside the range, the initial velocity will be decreased and the hitting feeling will be deteriorated.

The material hardness of the above mentioned intermediate layer is not particularly limited, but the Shore D Hardness is larger than or equal to 40, and preferably larger than or equal to 45. Also, its upper limit is particularly not limited, but preferably smaller than or equal to 70, and more preferably smaller than or equal to 65. If it is outside the range, the durability, particularly when hitting the driver, will be decreased.

When the sphere covered by the intermediate layer is covered by the outer most layer, the upper limit of the diameter of the covered sphere (in other words, the ball) is preferably smaller than or equal to 42.7 mm to comply with the golf rule. The thickness of the outer most layer is preferably larger or equal to 0.5 mm, and more preferably larger than or equal to 1.0 mm and the upper limit is smaller than or equal to 2.5 mm, and more preferably smaller than or equal to 2.0 mm. If it is outside the range, it will become difficult to form the multi-layer structure between the core and the outer most layer, and thus difficult to optimize the ball characteristic.

The material hardness of the above mentioned outer most layer is not particularly limited, but the Shore D Hardness is larger than or equal to 50, more preferably larger than or equal to 55. Also, its upper limit is not particularly limited, but it is preferable to smaller than or equal to 80, and more preferably smaller than or equal to 75. If it is outside the range, it will be easier for the surface of the ball to be damaged, and thus there will be cases in which the distance is decreased, or the hitting feeling is deteriorated.

Also, the material hardness of the above mentioned outer most layer (Shore D Hardness) is preferably set to be larger than the material hardness of the surrounding layer from the standpoint of making the ball characteristic better, especially making the spin characteristic better.

The deformation amount of the ball, when a specific load is applied, in other words, the deformation amount A when the initial load is 98 N (10 kgf) to the sphere and the ending load to the sphere is 5880 N (600 kgf), is preferably larger than or equal to 10.5 mm. The above mentioned load is substantially equal to the impact applied to the ball when hitting by the driver (#1 wood), and the entire ball is largely deformed. This can be an indicator for the hitting feeling at the time of the impact. If it is outside the range, there will be cases in which the hitting feeling towards the ball is hard.

Also, the deformation amount of the ball, when a specific load is applied, in other words, the deformation amount B of the ball when the initial load to the sphere is 98 N (10 kgf), and the ending load to the sphere is 4410 N (450 kgf), is preferably larger than or equal to 7.5 mm, more preferably larger than or equal to 8.4 mm, and the upper limit is smaller than or equal to 10 mm, more preferably smaller than or equal to 9.5 mm.

Also, the deformation amount C of the ball, when the initial load is 98 N (10 kgf) and the ending load is 1275 N (130 kgf), is smaller than or equal to 3.7 mm, and preferably smaller than or equal to 3.5 mm, while the lower limit, although not particularly limited, is larger than or equal to 2.5 mm, and more preferably larger than or equal to 2.7 mm.

On the surface of the cover, one or more than two kinds of multiple dimples can be formed. Further, on the surface of the cover, various paints can be applied. For the paint, because it is necessary to bear harsh environment in using the golf ball, two-component curable urethane paint, especially non-yellowing urethane paint can be preferably employed.

EXAMPLES

Hereinafter, Examples and Comparative Examples will be disclosed to describe the present invention in detail; however, the present invention is not limited to the embodiments below.

Examples 1 to 6, Comparative Examples 1 and 2

The inner core which is spherical is formed, after adjusting the rubber composition shown in Table 1. In other words, the primary vulcanization product (the inner half cup of semi vulcanization) is formed by kneading and mixing composition including the rubber material in Table 1 below, and then applying heat of 120° C. for 10 minutes. Next, the inner core including the infill shown in Table 2 is formed by including the material as the infill into the inner half cups being the hollow, and then performing the secondary vulcanization (full vulcanization) by applying the heat of 158° C. for 10 minutes in the metal mold. If there is no infill, the hollow remains.

Methods for making samples for each of the Examples and the Comparative Examples are described below. The half cups by the half vulcanization is formed by kneading and mixing the composition as to be the inner core, as a common method for each of Examples 1 to 6. Next, as shown in Table 2 below, various infills are filled into the hollow part of the inner core. Details will be described below. For Examples 1 and 5 (the inner core Nos. 1 and 5), the two half cups are bonded as a pair, and then, water or oil are filled into the center from a part of a bonding surface by an injector. Then, the secondary vulcanization is performed to obtain the inner core. For Examples 2 to 4 (the inner core Nos. 2 to 4), certain amount of gel A to C as materials of the center of the half cups are filled, and then the two half cups are bonded as a pair. Subsequently, the secondary vulcanization is performed to obtain the inner core. For Example 6 (the inner core No. 6), the two half cups are bonded as a pair and the secondary vulcanization is performed to obtain the inner core.

TABLE 1 Rubber for inner core (Mass Part) (Rubber I) Mixture of polybutadiene and natural rubber 100 Zinc oxide 4 Barium sulfate Specific gravity adjusted Anti-aging agent 0.1 Pentachlorothiophenol zinc salt 1 Zinc acrylate 36 Organic peroxide 1

The above mentioned composition of the rubber material (rubber I) is described below.

-   -   Polybutadiene rubber: trade name “BR51” (manufactured by JSR         Co.), polymerized by Nd-base catalyst     -   Zinc oxide: trade name “THREE ZINC OXIDE” (manufactured by Sakai         Chemical Industry Co.)     -   Barium sulfate: trade name “BARITE#100” (manufactured by Hakusui         Tech Co.)     -   Anti-aging agent: trade name “NOCRAC NS-6” (manufactured by         Ouchi Shinko Chemical Industrial)     -   Pentachlorothiophenol zinc salt: manufactured by Wako Pure         Chemical Industries Co.     -   Zinc acrylate: manufactured by Nippon Shokubai     -   Organic peroxide: dicumyl peroxide trade name “PERCMYL D”         (manufactured by NOF Co.) (the compounded amount of barium         sulfate is adjusted in a manner in which the mass (weight) of         the completed golf ball becomes 45.4 grams.)

TABLE 2 Inner Core No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Inner Core Structure Hollow Hollow Hollow Hollow Hollow Hollow Infill of hollow of Water Gel A Gel B Gel C Oil Air Inner Core Inner Core Composition Rubber I Rubber I Rubber I Rubber I Rubber I Rubber I Inner Core 23 23 23 23 23 23 Outer Diameter (mm) Inner Core 12 12 12 12 12 12 Inner Diameter (mm) The materials for the center are (1) to (5) below. (1) Gel A: polyvinyl alcoholic (PVA) gel (2) Gel B: cellulosic gel (3) Gel C: polyurethane gel (4) Oil: paraffin oil (5) Water: tap water

The common composition of the outer core is shown below. For the outer core of Examples 1 to 6, the rubber material (rubber II) of polybutadiene shown in Table 3 below is kneaded and mixed, and the primary vulcanization product (the outer half cups of half vulcanization) is formed by heating with 120° C. for 10 minutes. Next, the inner core after fully vulcanized is enclosed in the part which is hollow-shaped of the outer half cups, and is wrapped, and then the second vulcanization (full vulcanization) is performed by heating with 158° C. for 10 minutes in the metal mold, in order to obtain the core with the above mentioned material for the center filled, otherwise hollow in the center.

<Core of Comparative Example 1>

In Comparative Example 1, a single core is formed with an ordinary core made by rubber by using polybutadiene material (rubber II).

<The Inner Core and the Outer Core of Comparative Example 2>

In Comparative Example 2, the solid inner core is formed by injection molding by using resin material III shown in Table 3 below. The resin III is a material with 100 mass parts of thermoplastic polyester elastomer (trade name “HYTREL 3046”, manufactured by Toray DuPont Co.), which is same as resin material IV mentioned blow. The outer core is wrapped on the inner core, and the core is formed in the same manufacturing method and material of the outer core of the above mentioned Examples 1 to 6.

TABLE 3 (Mass Part) Rubber II Resin III Polybutadiene “BR51” 100 Zinc Oxide 4 Barium sulfate Specific Gravity Adjusted Anti-aging agent 0.1 Pentachlorothiophenol zinc salt 0.6 Zinc acrylate 31 Organic peroxide 1 HYTREL 3046 100 * The details of the above rubber material are same as rubber I above.

Next, with regards to each core, a multi-piece solid golf ball is obtained by inject-forming the common resin material (cover material) in each example shown in Table 4 below, and then forming surrounding layer 2, the inter mediate layer 3, and the outer most layer 4 in order around the core 10 as shown in FIG. 1. In this case, many dimples D are formed on the surface of the outer most layer 4.

TABLE 4 Composition (Mass Part) IV V VI HYTREL 3046 100 HPF 1000 100 HIMILAN 1605 50 AM 7329 50

The details of the materials in Table 4 are listed below.

-   -   “HYTEL 3046”: thermoplastic polyester elastomer manufactured by         Toray DuPont Co.     -   “HPF 1000”: ionomer manufactured by DuPont Co.     -   “HIMILAN 1605”: ionomer manufactured by Mitsui DuPont         Polychemical Co.     -   “AM 7329”: ionomer by Mitusi DuPont Polychemical Co.

For the above manufactured golf ball in each Example, the distance characteristic, the approach spin characteristic, and the hitting feeling are evaluated by the following method. The results are shown in Table 5 (Examples, Comparative Examples).

<Surface Hardness (S) of the Inner Core and the Surface Hardness (S) of the Outer Core>

Following JIS K6301-1975 standard, the surface hardness (S) of the inner core is evaluated by JIS-A Hardness, and the surface hardness (S) of the outer core is evaluated by JIS-C Hardness. In other words, based on JIS-A (measurement standard for the hardness of a general rubber), an indenter (denoted as push pin or indenter) is inserted to the surface of the inner core to deform, and deformation amount (pushing depth) is measured, and the surface hardness of the inner core is measured by quantifying by a durometer (spring-type rubber hardness measurer). With regards to JIS-C Hardness, like JIS-A above, the surface hardness (S) of the outer core is measured by a spring-type hardness measurer (JIS-C type) regulated by JIS K6301-1975.

<Material Hardness (Shore D Hardness) of Each Layer>

For the material hardness, measurement samples which are formed in sheet with thickness of 6 mm as measurement objects are measured by a type-D durometer complying with the ASTM-D2240.

<Compression Deformation Amount (Deformation Amount)>

The ball of each Example is compressed at 10 mm/min by using 4204 type manufactured by Instron Corporation, and the deformation amount (A) of the ball when the initial load is 98 N (10 kgf) and the ending load is 5880 N (600 kgf) is measured. Also, with the above mentioned measuring device, the deformation amount (B) of the ball when the initial load is 98 N (10 kgf) and the ending load is 4410 N (450 kgf) is measured. Further, the deformation amount (C) of the ball when the initial load is 98 N (10 kgf) and the ending load is 1275N (130 kgf) is measured.

<Initial Velocity of the Ball>

The initial velocity of the ball is measured by a drum rotation type of an initial velocity measuring device of USGA which R&A approves, and an initial velocity measuring device of the same type. The ball is adjusted in the temperature of 23±1° C. for three hours, and measured in a room with the temperature of 23±2° C. Ten balls are hit twice for each, and the initial velocity is measured by measuring the time in which the balls pass 6.28 feet (1.91 m).

<Distance Characteristic by Driver>

The total distance is measured, when the balls are hit by a hitting robot with a club “Tour Stage X-Drive 709” (manufactured by Bridgestone Sports Co., Ltd.) with a head speed (HS) 45 m/s. The spin amount is a value of the measurement of the ball right after the hitting by an initial-condition measurement device. A ball hitting angle is 10.5 degree.

Distance Characteristic by Irons

The total distance is measured, when the balls are hit by the hitting robot with a club “Tour Stage X-Blade 709 MC” (manufactured by Bridgestone Sports Co., Ltd.) with a head speed (HS) 45 m/s. These evaluations are made with the criteria below. The spin amount and hitting angle is same as above.

<Spin Characteristic of Approach Shots>

The spin amount right after the hitting is measured, when the balls are hit by the hitting robot with a sand wedge with a head speed (HS) 21 m/s, and its value is shown in the table below.

<Hitting Feeling>

Three top armature golfers evaluates, by following the below criteria, the hitting feeling when they hit the balls using a driver (#1 wood) with the head speed (HS) 42-50 m/s.

◯: Good hitting feeling x: Too hard, or too soft. “Good hitting feeling” above means moderate softness, and distinct comfortable hitting feeling.

TABLE 5 Example Comparative Example 1 2 3 4 5 6 1 2 Core Infill of Composition No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Single Hollow hollow Special gravity 1.0 1.26 1.04 1.04 1.1 0 rubber Resin III Inner Kind Rubber I Rubber I Rubber I Rubber I Rubber I Rubber I (rubber II) 23 core Outer diameter (mm) 23 23 23 23 23 23 12 Inner diameter (mm) 12 12 12 12 12 12 12 Surface hardness (S)(JIS-A) 75 75 75 75 75 75 75 Outer core Composition Rubber II Rubber II Rubber II Rubber II Rubber II Rubber II Rubber II Outer diameter (mm) 35.2 35.2 35.2 35.2 35.2 35.2 35.2 35.2 Surface hardness (JIS-C) 90 90 90 90 90 90 90 90 Cover Surrounding Material IV IV IV IV IV IV IV IV (each layer Thickness (mm) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 layer) Material hardness (Shore D) 30 30 30 30 30 30 30 30 Intermediate Material V V V V V V V V layer Thickness (mm) 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Material hardness (Shore D) 50 50 50 50 50 50 50 50 Outermost Material VI VI VI VI VI VI VI VI layer Thickness (mm) 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 Material hardness (Shore D) 64 64 64 64 64 64 64 64 Ball (A) Compression deformation amount (mm) 12.2 11.2 12.0 10.7 12.4 12.2 9.4 10.4 when 600 kg (B) Compression deformation amount (mm) 9.2 8.7 9.0 8.4 9.2 9.2 7.6 8.1 when 450 kg (C) Compression deformation amount (mm) 3.4 2.9 3.5 2.9 3.2 3.0 2.8 2.8 when 130 kg (A)/(C) 3.6 3.9 3.4 3.7 3.9 4.1 3.4 3.7 (B)/(C) 2.5 2.2 2.6 2.3 2.4 2.3 2.3 2.2 Ball Distance Initial velocity (m/s) 65.3 65 65.1 64.9 65.3 65.3 65.5 65.4 Charac- characteristic Spin (rpm) 3180 3095 3070 3089 3100 3300 3200 3143 teristic (W#1 HS Hitting angle (degree) 10.9 11.4 11.2 11.2 11.0 10.6 10.8 10.7 45 m/s) Carry (m) 223 217 217 215 218 220 223 222 Distance Initial velocity (m/s) 54.0 54.1 54.3 53.9 54.0 54.0 54.5 54.1 characteristic Spin (rpm) 5370 5095 5200 5290 5320 5390 5400 5350 (I#6) Carry (m) 162 167 165 165 161 163 163 160 Approach Spin (rpm) 5290 5180 5230 5220 5290 5300 5330 5300 spin characteristic (HS21 m/s) Hitting Driver Soft Soft Soft Soft Soft Soft Hard Hard feeling Iron Soft Soft Soft Soft Soft Soft Hard Hard

From the test data of Table 5 above, Comparative Examples 1 and 2 can maintain the distance characteristic and the approach shot spin characteristic, but cannot obtain the desired good hitting feeling. Thus, it can be understood that the advanced golfers and professional golfers are not satisfied. In contrast, Examples 1 to 6 can maintain the distance characteristic and the approach shot spin characteristic, and thus the professional golfers and the advanced golfers can obtain the comfortable hitting feeling.

The terms and descriptions used herein are used only for explanatory purposes and the present invention is not limited to them. Accordingly, the present invention allows various design-changes falling within the claimed scope of the present invention.

While the present invention may be embodied in many different forms, a number of illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein.

While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term “preferably” is non-exclusive and means “preferably, but not limited to.” In this disclosure and during the prosecution of this application, the terminology “present invention” or “invention” is meant as a non-specific, general reference and may be used as a reference to one or more aspects within the present disclosure. The language present invention or invention should not be improperly interpreted as an identification of criticality, should not be improperly interpreted as applying across all aspects or embodiments (i.e., it should be understood that the present invention has a number of aspects and embodiments), and should not be improperly interpreted as limiting the scope of the application or claims. In this disclosure and during the prosecution of this application, the terminology “embodiment” can be used to describe any aspect, feature, process or step, any combination thereof, and/or any portion thereof, etc. In some examples, various embodiments may include overlapping features. 

What is claimed is:
 1. A golf ball comprising: a spherical core; and a cover with one or more than two layers covering the core, wherein the core including two layers, one of which is an inner core being spherical and having an area in the center thereof, and the other of which is an outer core covering the inner core, the area being filled with at least one substance being different from a material of the inner core, value A is larger than or equal to 10.5, value C is smaller than or equal to 3.7, the value A is a deformation amount (mm) of the golf ball when an initial load is 98 N (10 kgf) and an ending load is 5880 N (600 kgf), and the value C is a deformation amount (mm) of the golf ball when an initial load is 98 N (10 kgf) and an ending load is 1275 N (130 kgf).
 2. The golf ball according to claim 1, wherein at least one substance being selected from a group consisting air, water, polyvinyl alcoholic (PVA) gel, cellulosic gel, oil state fluid, solid paraffin, and a jelly state food is filled in the area of the inner core.
 3. The golf ball according to claim 1, wherein the area of the inner core is a spherical space having a diameter between 5 and 18 mm.
 4. The golf ball according to claim 1, wherein an outer diameter of the inner core is between 15 and 25 mm.
 5. The golf ball according to claim 1, wherein a diameter of the core is between 34 and 40 mm.
 6. The golf ball according to claim 1, wherein surface hardness (S) of the inner core is between 30 and 90 in HS-A Hardness.
 7. The golf ball according to claim 1, wherein the cover covers the core with two layers, the two layers are, from inside, an intermediate layer, and an outer most layer.
 8. The golf ball according to claim 1, wherein the cover covers the core with three layers, the three layers are, from inside, a surrounding layer, an intermediate layer, and an outermost layer.
 9. The golf ball according to claim 8, wherein material hardness (Shore D Hardness) of the outer most layer is larger than material hardness of the surrounding layer. 